Magnetic core studies at LBNL and LLNL

Magnetic Core Studies at LBNL and LLNL A. W. Molvik a,* , A. Faltens b , L. Reginato b , M Blaszkiewicz c , C. Smith d , and R. Wood e LLNL, Livermore, CA 94550, USA LBNL, Berkeley, CA 94720, USA c Westinghouse, STC, 1310 Beulah Road, Pittsburgh, PA 15235-5098, USA d Nonvolatile Electronics, Inc., 11409 Valley View Road, Eden Prairie, MN 55433-3617 e National Magnetics, Inc., Adelanto, CA 92301 b a Abstract The objective of this work is to minimize the cost of the materials and maximize the performance of magnetic cores, a major cost component of a Heavy-Ion-Fusion, HIF, induction accelerator driver. This includes selection of the alloy for cost and performance, and maximizing the performance of each alloy evaluated. The two major performance parameters are the magnetic flux swing and the energy loss. The volt seconds of the cores, obtained from the flux swing with Faraday's Law, determines the beam energy and duration. Core losses from forming domains and moving their boundaries are a major factor in determining the efficiency of an induction accelerator. PACS numbers: 75.50Kj, 75.50.Bb, 75.60.Ej, 77.22.Jp * Corresponding author. Tel.: 510 422 9817; fax: 510 423 2664; e-mail: molvik1@llnl.gov. 1. Introduction A 5 MJ induction linac driver for HIF needs ~3 ∞ 10 7 kg of magnetic material.[1] To achieve a cost goal of <10 9 $US for a driver, core costs must be much less than the current ~100 $/kg in small quantities. A nearer term experiment being evaluated, needs ~2 ∞ 10 6 kg to deliver 25 kJ to a target.[2] Here also, cost reductions are important for achieving a marketable design. A recirculating induction accelerator passes the beam through each core many times, reducing the mass of cores required.[3] For a recirculator, core optimization emphasizes minimizing core energy losses more than minimizing initial cost. As have previous studies of magnetic materials, we have focused on amorphous alloys of steel that can be formed into ribbons of 15-25 µm thickness, at a much lower cost than by rolling.[4] The performance is significantly enhanced by magnetic annealing[5] where the ribbon is heated to ~360∞ C in an inert atmosphere while a magnetic field is applied parallel to the ribbon. If the material is annealed, prior to